According to Ashcroft's original concept,[1]} metallic atomic hydrogen should provide the acme of T\(_c\) , since the atom has the smallest mass, with highest frequencies if force constants are strong, and the potential for strong scattering of electrons by proton displacements seemed likely. Calculations sometimes including the quantum nature of the proton have predicted the stable structures versus pressure. The predictions are T\(_c\)  of 500K or higher,[2]} requiring pressures of 500 GPa or higher. Few attempts have reached a static pressure this high, so Ashcroft's second suggestion[3]} has been the avenue of choice: use H-rich molecules as the ambient pressure sample to avoid strong H\(_2\)  bonding and antibonding states being pulled away from the Fermi level, and to exploit precompression (higher H concentration and density).
